net/ipv4/netfilter/ip_conntrack_proto_tcp.c

   1 /* (C) 1999-2001 Paul `Rusty' Russell
   2  * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License version 2 as
   6  * published by the Free Software Foundation.
   7  *
   8  * Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>:
   9  *      - Real stateful connection tracking
  10  *      - Modified state transitions table
  11  *      - Window scaling support added
  12  *      - SACK support added
  13  *
  14  * Willy Tarreau:
  15  *      - State table bugfixes
  16  *      - More robust state changes
  17  *      - Tuning timer parameters
  18  *
  19  * version 2.2
  20  */
  21
  22 #include <linux/types.h>
  23 #include <linux/sched.h>
  24 #include <linux/timer.h>
  25 #include <linux/netfilter.h>
  26 #include <linux/module.h>
  27 #include <linux/in.h>
  28 #include <linux/ip.h>
  29 #include <linux/tcp.h>
  30 #include <linux/spinlock.h>
  31
  32 #include <net/tcp.h>
  33
  34 #include <linux/netfilter_ipv4.h>
  35 #include <linux/netfilter_ipv4/ip_conntrack.h>
  36 #include <linux/netfilter_ipv4/ip_conntrack_protocol.h>
  37
  38 #if 0
  39 #define DEBUGP printk
  40 #define DEBUGP_VARS
  41 #else
  42 #define DEBUGP(format, args...)
  43 #endif
  44
  45 /* Protects conntrack->proto.tcp */
  46 static DEFINE_RWLOCK(tcp_lock);
  47
  48 /* "Be conservative in what you do,
  49     be liberal in what you accept from others."
  50     If it's non-zero, we mark only out of window RST segments as INVALID. */
  51 int ip_ct_tcp_be_liberal __read_mostly = 0;
  52
  53 /* If it is set to zero, we disable picking up already established
  54    connections. */
  55 int ip_ct_tcp_loose __read_mostly = 1;
  56
  57 /* Max number of the retransmitted packets without receiving an (acceptable)
  58    ACK from the destination. If this number is reached, a shorter timer
  59    will be started. */
  60 int ip_ct_tcp_max_retrans __read_mostly = 3;
  61
  62   /* FIXME: Examine ipfilter's timeouts and conntrack transitions more
  63      closely.  They're more complex. --RR */
  64
  65 static const char *tcp_conntrack_names[] = {
  66         "NONE",
  67         "SYN_SENT",
  68         "SYN_RECV",
  69         "ESTABLISHED",
  70         "FIN_WAIT",
  71         "CLOSE_WAIT",
  72         "LAST_ACK",
  73         "TIME_WAIT",
  74         "CLOSE",
  75         "LISTEN"
  76 };
  77
  78 #define SECS * HZ
  79 #define MINS * 60 SECS
  80 #define HOURS * 60 MINS
  81 #define DAYS * 24 HOURS
  82
  83 unsigned int ip_ct_tcp_timeout_syn_sent __read_mostly =      2 MINS;
  84 unsigned int ip_ct_tcp_timeout_syn_recv __read_mostly =     60 SECS;
  85 unsigned int ip_ct_tcp_timeout_established __read_mostly =   5 DAYS;
  86 unsigned int ip_ct_tcp_timeout_fin_wait __read_mostly =      2 MINS;
  87 unsigned int ip_ct_tcp_timeout_close_wait __read_mostly =   60 SECS;
  88 unsigned int ip_ct_tcp_timeout_last_ack __read_mostly =     30 SECS;
  89 unsigned int ip_ct_tcp_timeout_time_wait __read_mostly =     2 MINS;
  90 unsigned int ip_ct_tcp_timeout_close __read_mostly =        10 SECS;
  91
  92 /* RFC1122 says the R2 limit should be at least 100 seconds.
  93    Linux uses 15 packets as limit, which corresponds
  94    to ~13-30min depending on RTO. */
  95 unsigned int ip_ct_tcp_timeout_max_retrans __read_mostly =   5 MINS;
  96
  97 static const unsigned int * tcp_timeouts[]
  98 = { NULL,                              /*      TCP_CONNTRACK_NONE */
  99     &ip_ct_tcp_timeout_syn_sent,       /*      TCP_CONNTRACK_SYN_SENT, */
 100     &ip_ct_tcp_timeout_syn_recv,       /*      TCP_CONNTRACK_SYN_RECV, */
 101     &ip_ct_tcp_timeout_established,    /*      TCP_CONNTRACK_ESTABLISHED,      */
 102     &ip_ct_tcp_timeout_fin_wait,       /*      TCP_CONNTRACK_FIN_WAIT, */
 103     &ip_ct_tcp_timeout_close_wait,     /*      TCP_CONNTRACK_CLOSE_WAIT,       */
 104     &ip_ct_tcp_timeout_last_ack,       /*      TCP_CONNTRACK_LAST_ACK, */
 105     &ip_ct_tcp_timeout_time_wait,      /*      TCP_CONNTRACK_TIME_WAIT,        */
 106     &ip_ct_tcp_timeout_close,          /*      TCP_CONNTRACK_CLOSE,    */
 107     NULL,                              /*      TCP_CONNTRACK_LISTEN */
 108  };
 109
 110 #define sNO TCP_CONNTRACK_NONE
 111 #define sSS TCP_CONNTRACK_SYN_SENT
 112 #define sSR TCP_CONNTRACK_SYN_RECV
 113 #define sES TCP_CONNTRACK_ESTABLISHED
 114 #define sFW TCP_CONNTRACK_FIN_WAIT
 115 #define sCW TCP_CONNTRACK_CLOSE_WAIT
 116 #define sLA TCP_CONNTRACK_LAST_ACK
 117 #define sTW TCP_CONNTRACK_TIME_WAIT
 118 #define sCL TCP_CONNTRACK_CLOSE
 119 #define sLI TCP_CONNTRACK_LISTEN
 120 #define sIV TCP_CONNTRACK_MAX
 121 #define sIG TCP_CONNTRACK_IGNORE
 122
 123 /* What TCP flags are set from RST/SYN/FIN/ACK. */
 124 enum tcp_bit_set {
 125         TCP_SYN_SET,
 126         TCP_SYNACK_SET,
 127         TCP_FIN_SET,
 128         TCP_ACK_SET,
 129         TCP_RST_SET,
 130         TCP_NONE_SET,
 131 };
 132
 133 /*
 134  * The TCP state transition table needs a few words...
 135  *
 136  * We are the man in the middle. All the packets go through us
 137  * but might get lost in transit to the destination.
 138  * It is assumed that the destinations can't receive segments
 139  * we haven't seen.
 140  *
 141  * The checked segment is in window, but our windows are *not*
 142  * equivalent with the ones of the sender/receiver. We always
 143  * try to guess the state of the current sender.
 144  *
 145  * The meaning of the states are:
 146  *
 147  * NONE:        initial state
 148  * SYN_SENT:    SYN-only packet seen
 149  * SYN_RECV:    SYN-ACK packet seen
 150  * ESTABLISHED: ACK packet seen
 151  * FIN_WAIT:    FIN packet seen
 152  * CLOSE_WAIT:  ACK seen (after FIN)
 153  * LAST_ACK:    FIN seen (after FIN)
 154  * TIME_WAIT:   last ACK seen
 155  * CLOSE:       closed connection
 156  *
 157  * LISTEN state is not used.
 158  *
 159  * Packets marked as IGNORED (sIG):
 160  *      if they may be either invalid or valid
 161  *      and the receiver may send back a connection
 162  *      closing RST or a SYN/ACK.
 163  *
 164  * Packets marked as INVALID (sIV):
 165  *      if they are invalid
 166  *      or we do not support the request (simultaneous open)
 167  */
 168 static const enum tcp_conntrack tcp_conntracks[2][6][TCP_CONNTRACK_MAX] = {
 169         {
 170 /* ORIGINAL */
 171 /*           sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI   */
 172 /*syn*/    { sSS, sSS, sIG, sIG, sIG, sIG, sIG, sSS, sSS, sIV },
 173 /*
 174  *      sNO -> sSS      Initialize a new connection
 175  *      sSS -> sSS      Retransmitted SYN
 176  *      sSR -> sIG      Late retransmitted SYN?
 177  *      sES -> sIG      Error: SYNs in window outside the SYN_SENT state
 178  *                      are errors. Receiver will reply with RST
 179  *                      and close the connection.
 180  *                      Or we are not in sync and hold a dead connection.
 181  *      sFW -> sIG
 182  *      sCW -> sIG
 183  *      sLA -> sIG
 184  *      sTW -> sSS      Reopened connection (RFC 1122).
 185  *      sCL -> sSS
 186  */
 187 /*           sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI   */
 188 /*synack*/ { sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV },
 189 /*
 190  * A SYN/ACK from the client is always invalid:
 191  *      - either it tries to set up a simultaneous open, which is
 192  *        not supported;
 193  *      - or the firewall has just been inserted between the two hosts
 194  *        during the session set-up. The SYN will be retransmitted
 195  *        by the true client (or it'll time out).
 196  */
 197 /*           sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI   */
 198 /*fin*/    { sIV, sIV, sFW, sFW, sLA, sLA, sLA, sTW, sCL, sIV },
 199 /*
 200  *      sNO -> sIV      Too late and no reason to do anything...
 201  *      sSS -> sIV      Client migth not send FIN in this state:
 202  *                      we enforce waiting for a SYN/ACK reply first.
 203  *      sSR -> sFW      Close started.
 204  *      sES -> sFW
 205  *      sFW -> sLA      FIN seen in both directions, waiting for
 206  *                      the last ACK.
 207  *                      Migth be a retransmitted FIN as well...
 208  *      sCW -> sLA
 209  *      sLA -> sLA      Retransmitted FIN. Remain in the same state.
 210  *      sTW -> sTW
 211  *      sCL -> sCL
 212  */
 213 /*           sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI   */
 214 /*ack*/    { sES, sIV, sES, sES, sCW, sCW, sTW, sTW, sCL, sIV },
 215 /*
 216  *      sNO -> sES      Assumed.
 217  *      sSS -> sIV      ACK is invalid: we haven't seen a SYN/ACK yet.
 218  *      sSR -> sES      Established state is reached.
 219  *      sES -> sES      :-)
 220  *      sFW -> sCW      Normal close request answered by ACK.
 221  *      sCW -> sCW
 222  *      sLA -> sTW      Last ACK detected.
 223  *      sTW -> sTW      Retransmitted last ACK. Remain in the same state.
 224  *      sCL -> sCL
 225  */
 226 /*           sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI   */
 227 /*rst*/    { sIV, sCL, sCL, sCL, sCL, sCL, sCL, sCL, sCL, sIV },
 228 /*none*/   { sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV }
 229         },
 230         {
 231 /* REPLY */
 232 /*           sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI   */
 233 /*syn*/    { sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV },
 234 /*
 235  *      sNO -> sIV      Never reached.
 236  *      sSS -> sIV      Simultaneous open, not supported
 237  *      sSR -> sIV      Simultaneous open, not supported.
 238  *      sES -> sIV      Server may not initiate a connection.
 239  *      sFW -> sIV
 240  *      sCW -> sIV
 241  *      sLA -> sIV
 242  *      sTW -> sIV      Reopened connection, but server may not do it.
 243  *      sCL -> sIV
 244  */
 245 /*           sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI   */
 246 /*synack*/ { sIV, sSR, sSR, sIG, sIG, sIG, sIG, sIG, sIG, sIV },
 247 /*
 248  *      sSS -> sSR      Standard open.
 249  *      sSR -> sSR      Retransmitted SYN/ACK.
 250  *      sES -> sIG      Late retransmitted SYN/ACK?
 251  *      sFW -> sIG      Might be SYN/ACK answering ignored SYN
 252  *      sCW -> sIG
 253  *      sLA -> sIG
 254  *      sTW -> sIG
 255  *      sCL -> sIG
 256  */
 257 /*           sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI   */
 258 /*fin*/    { sIV, sIV, sFW, sFW, sLA, sLA, sLA, sTW, sCL, sIV },
 259 /*
 260  *      sSS -> sIV      Server might not send FIN in this state.
 261  *      sSR -> sFW      Close started.
 262  *      sES -> sFW
 263  *      sFW -> sLA      FIN seen in both directions.
 264  *      sCW -> sLA
 265  *      sLA -> sLA      Retransmitted FIN.
 266  *      sTW -> sTW
 267  *      sCL -> sCL
 268  */
 269 /*           sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI   */
 270 /*ack*/    { sIV, sIG, sSR, sES, sCW, sCW, sTW, sTW, sCL, sIV },
 271 /*
 272  *      sSS -> sIG      Might be a half-open connection.
 273  *      sSR -> sSR      Might answer late resent SYN.
 274  *      sES -> sES      :-)
 275  *      sFW -> sCW      Normal close request answered by ACK.
 276  *      sCW -> sCW
 277  *      sLA -> sTW      Last ACK detected.
 278  *      sTW -> sTW      Retransmitted last ACK.
 279  *      sCL -> sCL
 280  */
 281 /*           sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sLI   */
 282 /*rst*/    { sIV, sCL, sCL, sCL, sCL, sCL, sCL, sCL, sCL, sIV },
 283 /*none*/   { sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV, sIV }
 284         }
 285 };
 286
 287 static int tcp_pkt_to_tuple(const struct sk_buff *skb,
 288                             unsigned int dataoff,
 289                             struct ip_conntrack_tuple *tuple)
 290 {
 291         struct tcphdr _hdr, *hp;
 292
 293         /* Actually only need first 8 bytes. */
 294         hp = skb_header_pointer(skb, dataoff, 8, &_hdr);
 295         if (hp == NULL)
 296                 return 0;
 297
 298         tuple->src.u.tcp.port = hp->source;
 299         tuple->dst.u.tcp.port = hp->dest;
 300
 301         return 1;
 302 }
 303
 304 static int tcp_invert_tuple(struct ip_conntrack_tuple *tuple,
 305                             const struct ip_conntrack_tuple *orig)
 306 {
 307         tuple->src.u.tcp.port = orig->dst.u.tcp.port;
 308         tuple->dst.u.tcp.port = orig->src.u.tcp.port;
 309         return 1;
 310 }
 311
 312 /* Print out the per-protocol part of the tuple. */
 313 static int tcp_print_tuple(struct seq_file *s,
 314                            const struct ip_conntrack_tuple *tuple)
 315 {
 316         return seq_printf(s, "sport=%hu dport=%hu ",
 317                           ntohs(tuple->src.u.tcp.port),
 318                           ntohs(tuple->dst.u.tcp.port));
 319 }
 320
 321 /* Print out the private part of the conntrack. */
 322 static int tcp_print_conntrack(struct seq_file *s,
 323                                const struct ip_conntrack *conntrack)
 324 {
 325         enum tcp_conntrack state;
 326
 327         read_lock_bh(&tcp_lock);
 328         state = conntrack->proto.tcp.state;
 329         read_unlock_bh(&tcp_lock);
 330
 331         return seq_printf(s, "%s ", tcp_conntrack_names[state]);
 332 }
 333
 334 #if defined(CONFIG_IP_NF_CONNTRACK_NETLINK) || \
 335     defined(CONFIG_IP_NF_CONNTRACK_NETLINK_MODULE)
 336 static int tcp_to_nfattr(struct sk_buff *skb, struct nfattr *nfa,
 337                          const struct ip_conntrack *ct)
 338 {
 339         struct nfattr *nest_parms;
 340
 341         read_lock_bh(&tcp_lock);
 342         nest_parms = NFA_NEST(skb, CTA_PROTOINFO_TCP);
 343         NFA_PUT(skb, CTA_PROTOINFO_TCP_STATE, sizeof(u_int8_t),
 344                 &ct->proto.tcp.state);
 345         read_unlock_bh(&tcp_lock);
 346
 347         NFA_NEST_END(skb, nest_parms);
 348
 349         return 0;
 350
 351 nfattr_failure:
 352         read_unlock_bh(&tcp_lock);
 353         return -1;
 354 }
 355
 356 static const size_t cta_min_tcp[CTA_PROTOINFO_TCP_MAX] = {
 357         [CTA_PROTOINFO_TCP_STATE-1]     = sizeof(u_int8_t),
 358 };
 359
 360 static int nfattr_to_tcp(struct nfattr *cda[], struct ip_conntrack *ct)
 361 {
 362         struct nfattr *attr = cda[CTA_PROTOINFO_TCP-1];
 363         struct nfattr *tb[CTA_PROTOINFO_TCP_MAX];
 364
 365         /* updates could not contain anything about the private
 366          * protocol info, in that case skip the parsing */
 367         if (!attr)
 368                 return 0;
 369
 370         nfattr_parse_nested(tb, CTA_PROTOINFO_TCP_MAX, attr);
 371
 372         if (nfattr_bad_size(tb, CTA_PROTOINFO_TCP_MAX, cta_min_tcp))
 373                 return -EINVAL;
 374
 375         if (!tb[CTA_PROTOINFO_TCP_STATE-1])
 376                 return -EINVAL;
 377
 378         write_lock_bh(&tcp_lock);
 379         ct->proto.tcp.state =
 380                 *(u_int8_t *)NFA_DATA(tb[CTA_PROTOINFO_TCP_STATE-1]);
 381         write_unlock_bh(&tcp_lock);
 382
 383         return 0;
 384 }
 385 #endif
 386
 387 static unsigned int get_conntrack_index(const struct tcphdr *tcph)
 388 {
 389         if (tcph->rst) return TCP_RST_SET;
 390         else if (tcph->syn) return (tcph->ack ? TCP_SYNACK_SET : TCP_SYN_SET);
 391         else if (tcph->fin) return TCP_FIN_SET;
 392         else if (tcph->ack) return TCP_ACK_SET;
 393         else return TCP_NONE_SET;
 394 }
 395
 396 /* TCP connection tracking based on 'Real Stateful TCP Packet Filtering
 397    in IP Filter' by Guido van Rooij.
 398
 399    http://www.nluug.nl/events/sane2000/papers.html
 400    http://www.iae.nl/users/guido/papers/tcp_filtering.ps.gz
 401
 402    The boundaries and the conditions are changed according to RFC793:
 403    the packet must intersect the window (i.e. segments may be
 404    after the right or before the left edge) and thus receivers may ACK
 405    segments after the right edge of the window.
 406
 407         td_maxend = max(sack + max(win,1)) seen in reply packets
 408         td_maxwin = max(max(win, 1)) + (sack - ack) seen in sent packets
 409         td_maxwin += seq + len - sender.td_maxend
 410                         if seq + len > sender.td_maxend
 411         td_end    = max(seq + len) seen in sent packets
 412
 413    I.   Upper bound for valid data:     seq <= sender.td_maxend
 414    II.  Lower bound for valid data:     seq + len >= sender.td_end - receiver.td_maxwin
 415    III. Upper bound for valid ack:      sack <= receiver.td_end
 416    IV.  Lower bound for valid ack:      ack >= receiver.td_end - MAXACKWINDOW
 417
 418    where sack is the highest right edge of sack block found in the packet.
 419
 420    The upper bound limit for a valid ack is not ignored -
 421    we doesn't have to deal with fragments.
 422 */
 423
 424 static inline __u32 segment_seq_plus_len(__u32 seq,
 425                                          size_t len,
 426                                          struct iphdr *iph,
 427                                          struct tcphdr *tcph)
 428 {
 429         return (seq + len - (iph->ihl + tcph->doff)*4
 430                 + (tcph->syn ? 1 : 0) + (tcph->fin ? 1 : 0));
 431 }
 432
 433 /* Fixme: what about big packets? */
 434 #define MAXACKWINCONST                  66000
 435 #define MAXACKWINDOW(sender)                                            \
 436         ((sender)->td_maxwin > MAXACKWINCONST ? (sender)->td_maxwin     \
 437                                               : MAXACKWINCONST)
 438
 439 /*
 440  * Simplified tcp_parse_options routine from tcp_input.c
 441  */
 442 static void tcp_options(const struct sk_buff *skb,
 443                         struct iphdr *iph,
 444                         struct tcphdr *tcph,
 445                         struct ip_ct_tcp_state *state)
 446 {
 447         unsigned char buff[(15 * 4) - sizeof(struct tcphdr)];
 448         unsigned char *ptr;
 449         int length = (tcph->doff*4) - sizeof(struct tcphdr);
 450
 451         if (!length)
 452                 return;
 453
 454         ptr = skb_header_pointer(skb,
 455                                  (iph->ihl * 4) + sizeof(struct tcphdr),
 456                                  length, buff);
 457         BUG_ON(ptr == NULL);
 458
 459         state->td_scale =
 460         state->flags = 0;
 461
 462         while (length > 0) {
 463                 int opcode=*ptr++;
 464                 int opsize;
 465
 466                 switch (opcode) {
 467                 case TCPOPT_EOL:
 468                         return;
 469                 case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
 470                         length--;
 471                         continue;
 472                 default:
 473                         opsize=*ptr++;
 474                         if (opsize < 2) /* "silly options" */
 475                                 return;
 476                         if (opsize > length)
 477                                 break;  /* don't parse partial options */
 478
 479                         if (opcode == TCPOPT_SACK_PERM
 480                             && opsize == TCPOLEN_SACK_PERM)
 481                                 state->flags |= IP_CT_TCP_FLAG_SACK_PERM;
 482                         else if (opcode == TCPOPT_WINDOW
 483                                  && opsize == TCPOLEN_WINDOW) {
 484                                 state->td_scale = *(u_int8_t *)ptr;
 485
 486                                 if (state->td_scale > 14) {
 487                                         /* See RFC1323 */
 488                                         state->td_scale = 14;
 489                                 }
 490                                 state->flags |=
 491                                         IP_CT_TCP_FLAG_WINDOW_SCALE;
 492                         }
 493                         ptr += opsize - 2;
 494                         length -= opsize;
 495                 }
 496         }
 497 }
 498
 499 static void tcp_sack(const struct sk_buff *skb,
 500                      struct iphdr *iph,
 501                      struct tcphdr *tcph,
 502                      __u32 *sack)
 503 {
 504         unsigned char buff[(15 * 4) - sizeof(struct tcphdr)];
 505         unsigned char *ptr;
 506         int length = (tcph->doff*4) - sizeof(struct tcphdr);
 507         __u32 tmp;
 508
 509         if (!length)
 510                 return;
 511
 512         ptr = skb_header_pointer(skb,
 513                                  (iph->ihl * 4) + sizeof(struct tcphdr),
 514                                  length, buff);
 515         BUG_ON(ptr == NULL);
 516
 517         /* Fast path for timestamp-only option */
 518         if (length == TCPOLEN_TSTAMP_ALIGNED*4
 519             && *(__be32 *)ptr ==
 520                 __constant_htonl((TCPOPT_NOP << 24)
 521                                  | (TCPOPT_NOP << 16)
 522                                  | (TCPOPT_TIMESTAMP << 8)
 523                                  | TCPOLEN_TIMESTAMP))
 524                 return;
 525
 526         while (length > 0) {
 527                 int opcode=*ptr++;
 528                 int opsize, i;
 529
 530                 switch (opcode) {
 531                 case TCPOPT_EOL:
 532                         return;
 533                 case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
 534                         length--;
 535                         continue;
 536                 default:
 537                         opsize=*ptr++;
 538                         if (opsize < 2) /* "silly options" */
 539                                 return;
 540                         if (opsize > length)
 541                                 break;  /* don't parse partial options */
 542
 543                         if (opcode == TCPOPT_SACK
 544                             && opsize >= (TCPOLEN_SACK_BASE
 545                                           + TCPOLEN_SACK_PERBLOCK)
 546                             && !((opsize - TCPOLEN_SACK_BASE)
 547                                  % TCPOLEN_SACK_PERBLOCK)) {
 548                                 for (i = 0;
 549                                      i < (opsize - TCPOLEN_SACK_BASE);
 550                                      i += TCPOLEN_SACK_PERBLOCK) {
 551                                         tmp = ntohl(*((__be32 *)(ptr+i)+1));
 552
 553                                         if (after(tmp, *sack))
 554                                                 *sack = tmp;
 555                                 }
 556                                 return;
 557                         }
 558                         ptr += opsize - 2;
 559                         length -= opsize;
 560                 }
 561         }
 562 }
 563
 564 static int tcp_in_window(struct ip_ct_tcp *state,
 565                          enum ip_conntrack_dir dir,
 566                          unsigned int index,
 567                          const struct sk_buff *skb,
 568                          struct iphdr *iph,
 569                          struct tcphdr *tcph)
 570 {
 571         struct ip_ct_tcp_state *sender = &state->seen[dir];
 572         struct ip_ct_tcp_state *receiver = &state->seen[!dir];
 573         __u32 seq, ack, sack, end, win, swin;
 574         int res;
 575
 576         /*
 577          * Get the required data from the packet.
 578          */
 579         seq = ntohl(tcph->seq);
 580         ack = sack = ntohl(tcph->ack_seq);
 581         win = ntohs(tcph->window);
 582         end = segment_seq_plus_len(seq, skb->len, iph, tcph);
 583
 584         if (receiver->flags & IP_CT_TCP_FLAG_SACK_PERM)
 585                 tcp_sack(skb, iph, tcph, &sack);
 586
 587         DEBUGP("tcp_in_window: START\n");
 588         DEBUGP("tcp_in_window: src=%u.%u.%u.%u:%hu dst=%u.%u.%u.%u:%hu "
 589                "seq=%u ack=%u sack=%u win=%u end=%u\n",
 590                 NIPQUAD(iph->saddr), ntohs(tcph->source),
 591                 NIPQUAD(iph->daddr), ntohs(tcph->dest),
 592                 seq, ack, sack, win, end);
 593         DEBUGP("tcp_in_window: sender end=%u maxend=%u maxwin=%u scale=%i "
 594                "receiver end=%u maxend=%u maxwin=%u scale=%i\n",
 595                 sender->td_end, sender->td_maxend, sender->td_maxwin,
 596                 sender->td_scale,
 597                 receiver->td_end, receiver->td_maxend, receiver->td_maxwin,
 598                 receiver->td_scale);
 599
 600         if (sender->td_end == 0) {
 601                 /*
 602                  * Initialize sender data.
 603                  */
 604                 if (tcph->syn && tcph->ack) {
 605                         /*
 606                          * Outgoing SYN-ACK in reply to a SYN.
 607                          */
 608                         sender->td_end =
 609                         sender->td_maxend = end;
 610                         sender->td_maxwin = (win == 0 ? 1 : win);
 611
 612                         tcp_options(skb, iph, tcph, sender);
 613                         /*
 614                          * RFC 1323:
 615                          * Both sides must send the Window Scale option
 616                          * to enable window scaling in either direction.
 617                          */
 618                         if (!(sender->flags & IP_CT_TCP_FLAG_WINDOW_SCALE
 619                               && receiver->flags & IP_CT_TCP_FLAG_WINDOW_SCALE))
 620                                 sender->td_scale =
 621                                 receiver->td_scale = 0;
 622                 } else {
 623                         /*
 624                          * We are in the middle of a connection,
 625                          * its history is lost for us.
 626                          * Let's try to use the data from the packet.
 627                          */
 628                         sender->td_end = end;
 629                         sender->td_maxwin = (win == 0 ? 1 : win);
 630                         sender->td_maxend = end + sender->td_maxwin;
 631                 }
 632         } else if (((state->state == TCP_CONNTRACK_SYN_SENT
 633                      && dir == IP_CT_DIR_ORIGINAL)
 634                     || (state->state == TCP_CONNTRACK_SYN_RECV
 635                         && dir == IP_CT_DIR_REPLY))
 636                     && after(end, sender->td_end)) {
 637                 /*
 638                  * RFC 793: "if a TCP is reinitialized ... then it need
 639                  * not wait at all; it must only be sure to use sequence
 640                  * numbers larger than those recently used."
 641                  */
 642                 sender->td_end =
 643                 sender->td_maxend = end;
 644                 sender->td_maxwin = (win == 0 ? 1 : win);
 645
 646                 tcp_options(skb, iph, tcph, sender);
 647         }
 648
 649         if (!(tcph->ack)) {
 650                 /*
 651                  * If there is no ACK, just pretend it was set and OK.
 652                  */
 653                 ack = sack = receiver->td_end;
 654         } else if (((tcp_flag_word(tcph) & (TCP_FLAG_ACK|TCP_FLAG_RST)) ==
 655                     (TCP_FLAG_ACK|TCP_FLAG_RST))
 656                    && (ack == 0)) {
 657                 /*
 658                  * Broken TCP stacks, that set ACK in RST packets as well
 659                  * with zero ack value.
 660                  */
 661                 ack = sack = receiver->td_end;
 662         }
 663
 664         if (seq == end
 665             && (!tcph->rst
 666                 || (seq == 0 && state->state == TCP_CONNTRACK_SYN_SENT)))
 667                 /*
 668                  * Packets contains no data: we assume it is valid
 669                  * and check the ack value only.
 670                  * However RST segments are always validated by their
 671                  * SEQ number, except when seq == 0 (reset sent answering
 672                  * SYN.
 673                  */
 674                 seq = end = sender->td_end;
 675
 676         DEBUGP("tcp_in_window: src=%u.%u.%u.%u:%hu dst=%u.%u.%u.%u:%hu "
 677                "seq=%u ack=%u sack =%u win=%u end=%u\n",
 678                 NIPQUAD(iph->saddr), ntohs(tcph->source),
 679                 NIPQUAD(iph->daddr), ntohs(tcph->dest),
 680                 seq, ack, sack, win, end);
 681         DEBUGP("tcp_in_window: sender end=%u maxend=%u maxwin=%u scale=%i "
 682                "receiver end=%u maxend=%u maxwin=%u scale=%i\n",
 683                 sender->td_end, sender->td_maxend, sender->td_maxwin,
 684                 sender->td_scale,
 685                 receiver->td_end, receiver->td_maxend, receiver->td_maxwin,
 686                 receiver->td_scale);
 687
 688         DEBUGP("tcp_in_window: I=%i II=%i III=%i IV=%i\n",
 689                 before(seq, sender->td_maxend + 1),
 690                 after(end, sender->td_end - receiver->td_maxwin - 1),
 691                 before(sack, receiver->td_end + 1),
 692                 after(ack, receiver->td_end - MAXACKWINDOW(sender)));
 693
 694         if (before(seq, sender->td_maxend + 1) &&
 695             after(end, sender->td_end - receiver->td_maxwin - 1) &&
 696             before(sack, receiver->td_end + 1) &&
 697             after(ack, receiver->td_end - MAXACKWINDOW(sender))) {
 698                 /*
 699                  * Take into account window scaling (RFC 1323).
 700                  */
 701                 if (!tcph->syn)
 702                         win <<= sender->td_scale;
 703
 704                 /*
 705                  * Update sender data.
 706                  */
 707                 swin = win + (sack - ack);
 708                 if (sender->td_maxwin < swin)
 709                         sender->td_maxwin = swin;
 710                 if (after(end, sender->td_end))
 711                         sender->td_end = end;
 712                 /*
 713                  * Update receiver data.
 714                  */
 715                 if (after(end, sender->td_maxend))
 716                         receiver->td_maxwin += end - sender->td_maxend;
 717                 if (after(sack + win, receiver->td_maxend - 1)) {
 718                         receiver->td_maxend = sack + win;
 719                         if (win == 0)
 720                                 receiver->td_maxend++;
 721                 }
 722
 723                 /*
 724                  * Check retransmissions.
 725                  */
 726                 if (index == TCP_ACK_SET) {
 727                         if (state->last_dir == dir
 728                             && state->last_seq == seq
 729                             && state->last_ack == ack
 730                             && state->last_end == end
 731                             && state->last_win == win)
 732                                 state->retrans++;
 733                         else {
 734                                 state->last_dir = dir;
 735                                 state->last_seq = seq;
 736                                 state->last_ack = ack;
 737                                 state->last_end = end;
 738                                 state->last_win = win;
 739                                 state->retrans = 0;
 740                         }
 741                 }
 742                 res = 1;
 743         } else {
 744                 res = 0;
 745                 if (sender->flags & IP_CT_TCP_FLAG_BE_LIBERAL ||
 746                     ip_ct_tcp_be_liberal)
 747                         res = 1;
 748                 if (!res && LOG_INVALID(IPPROTO_TCP))
 749                         nf_log_packet(PF_INET, 0, skb, NULL, NULL, NULL,
 750                         "ip_ct_tcp: %s ",
 751                         before(seq, sender->td_maxend + 1) ?
 752                         after(end, sender->td_end - receiver->td_maxwin - 1) ?
 753                         before(sack, receiver->td_end + 1) ?
 754                         after(ack, receiver->td_end - MAXACKWINDOW(sender)) ? "BUG"
 755                         : "ACK is under the lower bound (possible overly delayed ACK)"
 756                         : "ACK is over the upper bound (ACKed data not seen yet)"
 757                         : "SEQ is under the lower bound (already ACKed data retransmitted)"
 758                         : "SEQ is over the upper bound (over the window of the receiver)");
 759         }
 760
 761         DEBUGP("tcp_in_window: res=%i sender end=%u maxend=%u maxwin=%u "
 762                "receiver end=%u maxend=%u maxwin=%u\n",
 763                 res, sender->td_end, sender->td_maxend, sender->td_maxwin,
 764                 receiver->td_end, receiver->td_maxend, receiver->td_maxwin);
 765
 766         return res;
 767 }
 768
 769 #ifdef CONFIG_IP_NF_NAT_NEEDED
 770 /* Update sender->td_end after NAT successfully mangled the packet */
 771 void ip_conntrack_tcp_update(struct sk_buff *skb,
 772                              struct ip_conntrack *conntrack,
 773                              enum ip_conntrack_dir dir)
 774 {
 775         struct iphdr *iph = skb->nh.iph;
 776         struct tcphdr *tcph = (void *)skb->nh.iph + skb->nh.iph->ihl*4;
 777         __u32 end;
 778 #ifdef DEBUGP_VARS
 779         struct ip_ct_tcp_state *sender = &conntrack->proto.tcp.seen[dir];
 780         struct ip_ct_tcp_state *receiver = &conntrack->proto.tcp.seen[!dir];
 781 #endif
 782
 783         end = segment_seq_plus_len(ntohl(tcph->seq), skb->len, iph, tcph);
 784
 785         write_lock_bh(&tcp_lock);
 786         /*
 787          * We have to worry for the ack in the reply packet only...
 788          */
 789         if (after(end, conntrack->proto.tcp.seen[dir].td_end))
 790                 conntrack->proto.tcp.seen[dir].td_end = end;
 791         conntrack->proto.tcp.last_end = end;
 792         write_unlock_bh(&tcp_lock);
 793         DEBUGP("tcp_update: sender end=%u maxend=%u maxwin=%u scale=%i "
 794                "receiver end=%u maxend=%u maxwin=%u scale=%i\n",
 795                 sender->td_end, sender->td_maxend, sender->td_maxwin,
 796                 sender->td_scale,
 797                 receiver->td_end, receiver->td_maxend, receiver->td_maxwin,
 798                 receiver->td_scale);
 799 }
 800
 801 #endif
 802
 803 #define TH_FIN  0x01
 804 #define TH_SYN  0x02
 805 #define TH_RST  0x04
 806 #define TH_PUSH 0x08
 807 #define TH_ACK  0x10
 808 #define TH_URG  0x20
 809 #define TH_ECE  0x40
 810 #define TH_CWR  0x80
 811
 812 /* table of valid flag combinations - ECE and CWR are always valid */
 813 static const u8 tcp_valid_flags[(TH_FIN|TH_SYN|TH_RST|TH_PUSH|TH_ACK|TH_URG) + 1] =
 814 {
 815         [TH_SYN]                        = 1,
 816         [TH_SYN|TH_ACK]                 = 1,
 817         [TH_SYN|TH_PUSH]                = 1,
 818         [TH_SYN|TH_ACK|TH_PUSH]         = 1,
 819         [TH_RST]                        = 1,
 820         [TH_RST|TH_ACK]                 = 1,
 821         [TH_RST|TH_ACK|TH_PUSH]         = 1,
 822         [TH_FIN|TH_ACK]                 = 1,
 823         [TH_ACK]                        = 1,
 824         [TH_ACK|TH_PUSH]                = 1,
 825         [TH_ACK|TH_URG]                 = 1,
 826         [TH_ACK|TH_URG|TH_PUSH]         = 1,
 827         [TH_FIN|TH_ACK|TH_PUSH]         = 1,
 828         [TH_FIN|TH_ACK|TH_URG]          = 1,
 829         [TH_FIN|TH_ACK|TH_URG|TH_PUSH]  = 1,
 830 };
 831
 832 /* Protect conntrack agaist broken packets. Code taken from ipt_unclean.c.  */
 833 static int tcp_error(struct sk_buff *skb,
 834                      enum ip_conntrack_info *ctinfo,
 835                      unsigned int hooknum)
 836 {
 837         struct iphdr *iph = skb->nh.iph;
 838         struct tcphdr _tcph, *th;
 839         unsigned int tcplen = skb->len - iph->ihl * 4;
 840         u_int8_t tcpflags;
 841
 842         /* Smaller that minimal TCP header? */
 843         th = skb_header_pointer(skb, iph->ihl * 4,
 844                                 sizeof(_tcph), &_tcph);
 845         if (th == NULL) {
 846                 if (LOG_INVALID(IPPROTO_TCP))
 847                         nf_log_packet(PF_INET, 0, skb, NULL, NULL, NULL,
 848                                 "ip_ct_tcp: short packet ");
 849                 return -NF_ACCEPT;
 850         }
 851
 852         /* Not whole TCP header or malformed packet */
 853         if (th->doff*4 < sizeof(struct tcphdr) || tcplen < th->doff*4) {
 854                 if (LOG_INVALID(IPPROTO_TCP))
 855                         nf_log_packet(PF_INET, 0, skb, NULL, NULL, NULL,
 856                                 "ip_ct_tcp: truncated/malformed packet ");
 857                 return -NF_ACCEPT;
 858         }
 859
 860         /* Checksum invalid? Ignore.
 861          * We skip checking packets on the outgoing path
 862          * because it is assumed to be correct.
 863          */
 864         /* FIXME: Source route IP option packets --RR */
 865         if (ip_conntrack_checksum && hooknum == NF_IP_PRE_ROUTING &&
 866             nf_ip_checksum(skb, hooknum, iph->ihl * 4, IPPROTO_TCP)) {
 867                 if (LOG_INVALID(IPPROTO_TCP))
 868                         nf_log_packet(PF_INET, 0, skb, NULL, NULL, NULL,
 869                                   "ip_ct_tcp: bad TCP checksum ");
 870                 return -NF_ACCEPT;
 871         }
 872
 873         /* Check TCP flags. */
 874         tcpflags = (((u_int8_t *)th)[13] & ~(TH_ECE|TH_CWR));
 875         if (!tcp_valid_flags[tcpflags]) {
 876                 if (LOG_INVALID(IPPROTO_TCP))
 877                         nf_log_packet(PF_INET, 0, skb, NULL, NULL, NULL,
 878                                   "ip_ct_tcp: invalid TCP flag combination ");
 879                 return -NF_ACCEPT;
 880         }
 881
 882         return NF_ACCEPT;
 883 }
 884
 885 /* Returns verdict for packet, or -1 for invalid. */
 886 static int tcp_packet(struct ip_conntrack *conntrack,
 887                       const struct sk_buff *skb,
 888                       enum ip_conntrack_info ctinfo)
 889 {
 890         enum tcp_conntrack new_state, old_state;
 891         enum ip_conntrack_dir dir;
 892         struct iphdr *iph = skb->nh.iph;
 893         struct tcphdr *th, _tcph;
 894         unsigned long timeout;
 895         unsigned int index;
 896
 897         th = skb_header_pointer(skb, iph->ihl * 4,
 898                                 sizeof(_tcph), &_tcph);
 899         BUG_ON(th == NULL);
 900
 901         write_lock_bh(&tcp_lock);
 902         old_state = conntrack->proto.tcp.state;
 903         dir = CTINFO2DIR(ctinfo);
 904         index = get_conntrack_index(th);
 905         new_state = tcp_conntracks[dir][index][old_state];
 906
 907         switch (new_state) {
 908         case TCP_CONNTRACK_IGNORE:
 909                 /* Ignored packets:
 910                  *
 911                  * a) SYN in ORIGINAL
 912                  * b) SYN/ACK in REPLY
 913                  * c) ACK in reply direction after initial SYN in original.
 914                  */
 915                 if (index == TCP_SYNACK_SET
 916                     && conntrack->proto.tcp.last_index == TCP_SYN_SET
 917                     && conntrack->proto.tcp.last_dir != dir
 918                     && ntohl(th->ack_seq) ==
 919                              conntrack->proto.tcp.last_end) {
 920                         /* This SYN/ACK acknowledges a SYN that we earlier
 921                          * ignored as invalid. This means that the client and
 922                          * the server are both in sync, while the firewall is
 923                          * not. We kill this session and block the SYN/ACK so
 924                          * that the client cannot but retransmit its SYN and
 925                          * thus initiate a clean new session.
 926                          */
 927                         write_unlock_bh(&tcp_lock);
 928                         if (LOG_INVALID(IPPROTO_TCP))
 929                                 nf_log_packet(PF_INET, 0, skb, NULL, NULL,
 930                                               NULL, "ip_ct_tcp: "
 931                                               "killing out of sync session ");
 932                         if (del_timer(&conntrack->timeout))
 933                                 conntrack->timeout.function((unsigned long)
 934                                                             conntrack);
 935                         return -NF_DROP;
 936                 }
 937                 conntrack->proto.tcp.last_index = index;
 938                 conntrack->proto.tcp.last_dir = dir;
 939                 conntrack->proto.tcp.last_seq = ntohl(th->seq);
 940                 conntrack->proto.tcp.last_end =
 941                     segment_seq_plus_len(ntohl(th->seq), skb->len, iph, th);
 942
 943                 write_unlock_bh(&tcp_lock);
 944                 if (LOG_INVALID(IPPROTO_TCP))
 945                         nf_log_packet(PF_INET, 0, skb, NULL, NULL, NULL,
 946                                   "ip_ct_tcp: invalid packet ignored ");
 947                 return NF_ACCEPT;
 948         case TCP_CONNTRACK_MAX:
 949                 /* Invalid packet */
 950                 DEBUGP("ip_ct_tcp: Invalid dir=%i index=%u ostate=%u\n",
 951                        dir, get_conntrack_index(th),
 952                        old_state);
 953                 write_unlock_bh(&tcp_lock);
 954                 if (LOG_INVALID(IPPROTO_TCP))
 955                         nf_log_packet(PF_INET, 0, skb, NULL, NULL, NULL,
 956                                   "ip_ct_tcp: invalid state ");
 957                 return -NF_ACCEPT;
 958         case TCP_CONNTRACK_SYN_SENT:
 959                 if (old_state < TCP_CONNTRACK_TIME_WAIT)
 960                         break;
 961                 if ((conntrack->proto.tcp.seen[dir].flags &
 962                          IP_CT_TCP_FLAG_CLOSE_INIT)
 963                     || after(ntohl(th->seq),
 964                              conntrack->proto.tcp.seen[dir].td_end)) {
 965                         /* Attempt to reopen a closed connection.
 966                         * Delete this connection and look up again. */
 967                         write_unlock_bh(&tcp_lock);
 968                         if (del_timer(&conntrack->timeout))
 969                                 conntrack->timeout.function((unsigned long)
 970                                                             conntrack);
 971                         return -NF_REPEAT;
 972                 } else {
 973                         write_unlock_bh(&tcp_lock);
 974                         if (LOG_INVALID(IPPROTO_TCP))
 975                                 nf_log_packet(PF_INET, 0, skb, NULL, NULL,
 976                                               NULL, "ip_ct_tcp: invalid SYN");
 977                         return -NF_ACCEPT;
 978                 }
 979         case TCP_CONNTRACK_CLOSE:
 980                 if (index == TCP_RST_SET
 981                     && ((test_bit(IPS_SEEN_REPLY_BIT, &conntrack->status)
 982                          && conntrack->proto.tcp.last_index == TCP_SYN_SET)
 983                         || (!test_bit(IPS_ASSURED_BIT, &conntrack->status)
 984                             && conntrack->proto.tcp.last_index == TCP_ACK_SET))
 985                     && ntohl(th->ack_seq) == conntrack->proto.tcp.last_end) {
 986                         /* RST sent to invalid SYN or ACK we had let through
 987                          * at a) and c) above:
 988                          *
 989                          * a) SYN was in window then
 990                          * c) we hold a half-open connection.
 991                          *
 992                          * Delete our connection entry.
 993                          * We skip window checking, because packet might ACK
 994                          * segments we ignored. */
 995                         goto in_window;
 996                 }
 997                 /* Just fall through */
 998         default:
 999                 /* Keep compilers happy. */
1000                 break;
1001         }
1002
1003         if (!tcp_in_window(&conntrack->proto.tcp, dir, index,
1004                            skb, iph, th)) {
1005                 write_unlock_bh(&tcp_lock);
1006                 return -NF_ACCEPT;
1007         }
1008     in_window:
1009         /* From now on we have got in-window packets */
1010         conntrack->proto.tcp.last_index = index;
1011
1012         DEBUGP("tcp_conntracks: src=%u.%u.%u.%u:%hu dst=%u.%u.%u.%u:%hu "
1013                "syn=%i ack=%i fin=%i rst=%i old=%i new=%i\n",
1014                 NIPQUAD(iph->saddr), ntohs(th->source),
1015                 NIPQUAD(iph->daddr), ntohs(th->dest),
1016                 (th->syn ? 1 : 0), (th->ack ? 1 : 0),
1017                 (th->fin ? 1 : 0), (th->rst ? 1 : 0),
1018                 old_state, new_state);
1019
1020         conntrack->proto.tcp.state = new_state;
1021         if (old_state != new_state
1022             && (new_state == TCP_CONNTRACK_FIN_WAIT
1023                 || new_state == TCP_CONNTRACK_CLOSE))
1024                 conntrack->proto.tcp.seen[dir].flags |= IP_CT_TCP_FLAG_CLOSE_INIT;
1025         timeout = conntrack->proto.tcp.retrans >= ip_ct_tcp_max_retrans
1026                   && *tcp_timeouts[new_state] > ip_ct_tcp_timeout_max_retrans
1027                   ? ip_ct_tcp_timeout_max_retrans : *tcp_timeouts[new_state];
1028         write_unlock_bh(&tcp_lock);
1029
1030         ip_conntrack_event_cache(IPCT_PROTOINFO_VOLATILE, skb);
1031         if (new_state != old_state)
1032                 ip_conntrack_event_cache(IPCT_PROTOINFO, skb);
1033
1034         if (!test_bit(IPS_SEEN_REPLY_BIT, &conntrack->status)) {
1035                 /* If only reply is a RST, we can consider ourselves not to
1036                    have an established connection: this is a fairly common
1037                    problem case, so we can delete the conntrack
1038                    immediately.  --RR */
1039                 if (th->rst) {
1040                         if (del_timer(&conntrack->timeout))
1041                                 conntrack->timeout.function((unsigned long)
1042                                                             conntrack);
1043                         return NF_ACCEPT;
1044                 }
1045         } else if (!test_bit(IPS_ASSURED_BIT, &conntrack->status)
1046                    && (old_state == TCP_CONNTRACK_SYN_RECV
1047                        || old_state == TCP_CONNTRACK_ESTABLISHED)
1048                    && new_state == TCP_CONNTRACK_ESTABLISHED) {
1049                 /* Set ASSURED if we see see valid ack in ESTABLISHED
1050                    after SYN_RECV or a valid answer for a picked up
1051                    connection. */
1052                 set_bit(IPS_ASSURED_BIT, &conntrack->status);
1053                 ip_conntrack_event_cache(IPCT_STATUS, skb);
1054         }
1055         ip_ct_refresh_acct(conntrack, ctinfo, skb, timeout);
1056
1057         return NF_ACCEPT;
1058 }
1059
1060 /* Called when a new connection for this protocol found. */
1061 static int tcp_new(struct ip_conntrack *conntrack,
1062                    const struct sk_buff *skb)
1063 {
1064         enum tcp_conntrack new_state;
1065         struct iphdr *iph = skb->nh.iph;
1066         struct tcphdr *th, _tcph;
1067 #ifdef DEBUGP_VARS
1068         struct ip_ct_tcp_state *sender = &conntrack->proto.tcp.seen[0];
1069         struct ip_ct_tcp_state *receiver = &conntrack->proto.tcp.seen[1];
1070 #endif
1071
1072         th = skb_header_pointer(skb, iph->ihl * 4,
1073                                 sizeof(_tcph), &_tcph);
1074         BUG_ON(th == NULL);
1075
1076         /* Don't need lock here: this conntrack not in circulation yet */
1077         new_state
1078                 = tcp_conntracks[0][get_conntrack_index(th)]
1079                 [TCP_CONNTRACK_NONE];
1080
1081         /* Invalid: delete conntrack */
1082         if (new_state >= TCP_CONNTRACK_MAX) {
1083                 DEBUGP("ip_ct_tcp: invalid new deleting.\n");
1084                 return 0;
1085         }
1086
1087         if (new_state == TCP_CONNTRACK_SYN_SENT) {
1088                 /* SYN packet */
1089                 conntrack->proto.tcp.seen[0].td_end =
1090                         segment_seq_plus_len(ntohl(th->seq), skb->len,
1091                                              iph, th);
1092                 conntrack->proto.tcp.seen[0].td_maxwin = ntohs(th->window);
1093                 if (conntrack->proto.tcp.seen[0].td_maxwin == 0)
1094                         conntrack->proto.tcp.seen[0].td_maxwin = 1;
1095                 conntrack->proto.tcp.seen[0].td_maxend =
1096                         conntrack->proto.tcp.seen[0].td_end;
1097
1098                 tcp_options(skb, iph, th, &conntrack->proto.tcp.seen[0]);
1099                 conntrack->proto.tcp.seen[1].flags = 0;
1100         } else if (ip_ct_tcp_loose == 0) {
1101                 /* Don't try to pick up connections. */
1102                 return 0;
1103         } else {
1104                 /*
1105                  * We are in the middle of a connection,
1106                  * its history is lost for us.
1107                  * Let's try to use the data from the packet.
1108                  */
1109                 conntrack->proto.tcp.seen[0].td_end =
1110                         segment_seq_plus_len(ntohl(th->seq), skb->len,
1111                                              iph, th);
1112                 conntrack->proto.tcp.seen[0].td_maxwin = ntohs(th->window);
1113                 if (conntrack->proto.tcp.seen[0].td_maxwin == 0)
1114                         conntrack->proto.tcp.seen[0].td_maxwin = 1;
1115                 conntrack->proto.tcp.seen[0].td_maxend =
1116                         conntrack->proto.tcp.seen[0].td_end +
1117                         conntrack->proto.tcp.seen[0].td_maxwin;
1118                 conntrack->proto.tcp.seen[0].td_scale = 0;
1119
1120                 /* We assume SACK and liberal window checking to handle
1121                  * window scaling */
1122                 conntrack->proto.tcp.seen[0].flags =
1123                 conntrack->proto.tcp.seen[1].flags = IP_CT_TCP_FLAG_SACK_PERM |
1124                                                      IP_CT_TCP_FLAG_BE_LIBERAL;
1125         }
1126
1127         conntrack->proto.tcp.seen[1].td_end = 0;
1128         conntrack->proto.tcp.seen[1].td_maxend = 0;
1129         conntrack->proto.tcp.seen[1].td_maxwin = 1;
1130         conntrack->proto.tcp.seen[1].td_scale = 0;
1131
1132         /* tcp_packet will set them */
1133         conntrack->proto.tcp.state = TCP_CONNTRACK_NONE;
1134         conntrack->proto.tcp.last_index = TCP_NONE_SET;
1135
1136         DEBUGP("tcp_new: sender end=%u maxend=%u maxwin=%u scale=%i "
1137                "receiver end=%u maxend=%u maxwin=%u scale=%i\n",
1138                 sender->td_end, sender->td_maxend, sender->td_maxwin,
1139                 sender->td_scale,
1140                 receiver->td_end, receiver->td_maxend, receiver->td_maxwin,
1141                 receiver->td_scale);
1142         return 1;
1143 }
1144
1145 struct ip_conntrack_protocol ip_conntrack_protocol_tcp =
1146 {
1147         .proto                  = IPPROTO_TCP,
1148         .name                   = "tcp",
1149         .pkt_to_tuple           = tcp_pkt_to_tuple,
1150         .invert_tuple           = tcp_invert_tuple,
1151         .print_tuple            = tcp_print_tuple,
1152         .print_conntrack        = tcp_print_conntrack,
1153         .packet                 = tcp_packet,
1154         .new                    = tcp_new,
1155         .error                  = tcp_error,
1156 #if defined(CONFIG_IP_NF_CONNTRACK_NETLINK) || \
1157     defined(CONFIG_IP_NF_CONNTRACK_NETLINK_MODULE)
1158         .to_nfattr              = tcp_to_nfattr,
1159         .from_nfattr            = nfattr_to_tcp,
1160         .tuple_to_nfattr        = ip_ct_port_tuple_to_nfattr,
1161         .nfattr_to_tuple        = ip_ct_port_nfattr_to_tuple,
1162 #endif
1163 };